The present invention relates to a projection television receiver having three projection tubes for projecting red, green, and blue images, respectively, onto a common screen composed of a Fresnel lens or lenticular lens. More particularly, the invention relates to improvements in a coupler for filling cooling liquid between the lens and the front face of each projection tube.
Referring to FIG. 6, there is shown a conventional projection apparatus for use with a projection television receiver. The apparatus supports a projection tube 1. A cooling liquid is filled between the front face of the tube 1 and a lens 7. A metallic shield plate 3 is mounted on the side surface of the tube 1. Projections 1a are formed on the rear surface of the tube 1. A metallic presser plate 5 is pressed against each projection 1a via a resilient member 4.
A coupler 6 has a window on its front side. A lens 7 is mounted in the window. The coupler 6 is attached to the front face of the tube 1 via a packing 8. The presser plates 5 are provided with holes 5a into which screws 10 are inserted via springs 9, the holes 5a being spaced 90.degree. from each other. The coupler 6 has four tapped holes spaced 90.degree. from each other. The screws 10 are engaged in the tapped holes. The screws 10 are tightened to cause the springs 9 to press the coupler 6 against the front face of the tube 1. The packing 8 is used to seal the coupler 6 to the tube 1. The sealed inside of the coupler 6 between the lens 7 and the tube 1 is filled with cooling liquid to cool the image surface of the tube 1. Cooling fins are mounted on the outer surface of the liquid-holding portion of the coupler 6. The inner surface of the holding portion is smooth.
Accordingly, most of the light rays exiting the imaged surface of the projection tube 1 pass through the lens 7, but some rays impact the smooth inner surface of the coupler 6 and are reflected. As a result, a portion of the reflected light passes through the screen, thus creating a ghost.
Heat is dissipated into the cooling liquid, causing convection of the liquid. However, the flow of the liquid is irregular. Further, the surface area of the coupler 6 that can contact the liquid is limited because the inner surface of the coupler 6 is smooth. For these reasons, heat is not readily transmitted to the coupler 6 from the cooling liquid. Consequently, the tube is not cooled sufficiently.